We are closing this clinical protocol due to supply chain issues. We are no longer able to obtain the intranasal delivery device.

The purpose of this study is to find out whether insulin, a drug approved by the FDA for the treatment of diabetes mellitus, reaches the brain and spinal cord when delivered as a nasal spray (intranasally). Intranasal insulin has been shown to improve memory and mood in patients with neurological diseases such as mild cognitive impairment and dementia, but more evidence is needed to support the ability to effectively target the brain through intranasal routes.

18 healthy middle-aged adults will be randomly assigned to receive a single intranasal dose of 40 units insulin ("low dose" group), 80 units insulin ("high dose" group), or saline (placebo, or control group). Participants will undergo an image-guided lumbar puncture (spinal tap) performed by a study clinician. Samples of cerebrospinal fluid (a fluid surrounding the brain and spinal cord) and blood will be collected at 5 timepoints during the lumbar puncture: once prior to the administration of intranasal insulin, and again at 10, 20, 30, and 40 minutes after the dose is given. Samples will be tested to determine the level of insulin detected in the cerebrospinal fluid and blood at each time point. Results of this study will provide essential information about the ability of insulin to reach the brain after intranasal administration.

Inclusion Criteria:

1. Subject is between ≥36 and ≤ 55 years of age
2. Subject's BMI is between >=18.5 and <=24.9, or can safely undergo a lumbar puncture at the discretion of the radiologist
3. MOCA score ≥26
4. Subject must be proficient in speaking English to comply with instructions and measures for the study
5. Subject can provide written informed consent
6. Female subjects must have either: (1) a negative pregnancy test at the screening visit and treatment visit OR (2) be at least 2 years post-menopausal / surgically sterile.

Exclusion Criteria:

1. Subject has medical history and/or clinically determined disorders: chronic sinusitis, previous nasal and/or oto-pharyngeal surgery and severe deviated septum and/or other anomalies.
2. Subject has history of any of the following: active and significant central nervous system, psychiatric illness, pulmonary, or cardiovascular disorders or any other clinically relevant abnormality that inclusion would pose a safety risk to the subject as determined by investigator
3. Subject has participated in a clinical trial investigation within 3 months of this study.
4. Subject has an insulin allergy
5. Subject has Insulin-dependent diabetes
6. Subject is pregnant or breast feeding
7. Contraindication to spinal tap or other safety factors that preclude lumbar puncture in the investigator's opinion
8. Any other clinically relevant finding that would pose a safety risk to the subject as determined by the investigator

Single-blind